Low frequency drill bit apparatus and method of locating the position of the drill head below the surface of the earth

ABSTRACT

An earth drill bit locating apparatus and method of detecting and locating the position of a drill bit below the surface of the earth utilizing very low frequency electromagnetic energy. The apparatus includes a transmitter located adjacent the drill bit for transmitting a very low-frequency electromagnetic wave below 5,000 Hz and a plurality of receivers including antennae placed adjacent to the earth&#39;&#39;s surface for detecting the low-frequency wave and computing the position of the drill bit by triangulation. Each receiver is a directional indicating receiving means for obtaining raw data in order to display and plot the movement of the drill head as it moves into the earth. The transmitter is powered by an alternator driven by a turbine in the mud supply conduit or collar just above the bit. The drill collar is fitted with electrodes or wire loops which are connected to the transmitter output to cause the drill collar to act as an electric or magnetic radiating dipole.

Elite Sttes Elwood 11] 3,28,87 [451 Aug. 13, 1974 [76] Inventor: AlbertA. Elwood, PO. Box 10592,

Riviera Beach, Fla. 33404 22 Filed: May 15, 1972 21 Appl.No.:253,544,

52 us. Cl. 175/45, 175/61 51 Int. Cl E2lb 47/024 [58] Field of Search175/1, 61, 73, 40, 45, 175/24; 102/2l.6

[56] References Cited UNITED STATES PATENTS 3,100,444 8/1963 Ball et a1102/21.6

3,406,766 10/1968 Henderson 175/61 3,461,979 8/1969 Newfarmer 175/453,465,834 9/1969 Southworth 175/73 X 3,529,682 9/1970 Coyne et a1 175/453,693,142 9/1972 Jones 175/45 X 3,712,391 1/1973 Coyne 175/45 X3,722,605 3/1973 lsham 175/40 3,739,871 6/1973 Bailey 175/1 X PrimaryExaminer-David H. Brown Attorney, Agent, or Firm-Malin & Haley [5 7]ABSTRACT An earth drill bit locating apparatus and method of detectingand locating the position of a drill bit below the surface of the earthutilizing very low frequency electromagnetic energy. The apparatusincludes a transmitter located adjacent the drill bit for transmitting avery low-frequency electromagnetic wave below 5,000 Hz and a pluralityof receivers including antennae placed adjacent to the earths surfacefor detecting the low-frequency wave and computing the position of thedrill bit by triangulation. Each receiver is a directional indicatingreceiving means for obtaining raw data in order to display and plot themovement of the drill head as it moves into the earth. The transmitteris powered by an alternator driven by a turbine in the mud supplyconduit or collar just above the bit. The drill collar is fitted withelectrodes or wire loops which are connected to the transmitter outputto cause the drill collar to act as an electric or magnetic radiatingdipole.

7 Claims, 5 Drawing Figures PATENIEUAum 31314 $828,867,

FlG. IA

FIG. 2 24 Pmm naus 1 31974 SHEET 2 [IF 3 III N 3 65 ENEQQ W m. 20E

LOW FREQUENCY DRILL BIT APPARATUS AND METHOD OF LOCATING THE POSITION OFTHE DRILL HEAD BELOW THE SURFACE OF THE EARTH BACKGROUND OF THEINVENTION This invention relates to apparatus and a method for locatingand tracking drill bits as they pass through the earth, and, moreparticularly, to an apparatus and method utilizing a transmitted energywave frequency of less than 5,000 Hz.

In the past, gyroscopic survey instruments were built for directionallysurveying boreholes. Also single and multiple magnetic methods oforientation have been utilized in conjunction with non-magnetic drillcollars. Such devices require the drill string to be pulled out of thedrill hole or the drilling operation stopped while survey devices werelowered into the string down to the non-magnetic drill collar. Theseoperations contribute heavily to the expense of drilling a well.

BRIEF DESCRIPTION OF THE INVENTION The present invention relates to anew and improved low frequency drill bit locating and tracking apparatusand method of detecting the location of a drill collar as it movesthrough the earth by transmitting and receiving a low-frequencyelectro-magnetic wave below 5,000 Hz. The transmitter is placed adjacentthe drill bit in the drill collar. The transmitter includes analternator driven by a turbine in the mud supply conduit in the drillcollar. The alternator functions as the transmitter for continuousoperation during the drilling operation. The transmitter may also be abattery powered very low-frequency power oscillator. The drill collar isfitted with two electrodes or a wire loop connected to the transmitteroutput to cause the drill collar to act as an electrical or magneticdipole. A plurality of directional indicating receivers with a magneticor electric dipole antenna systems located in the lowfrequency signaland the direction of the signal. A computing means is utilized tomanipulate the data in order to plot the movement of the drill collar bytriangulation.

The method of operation is to place three receivers at known points withrespect to the well head which acts as a reference for the system. Thearrangement of the three receivers is basically an equilateral trianglewith the well head in the center. All relative angles and distancesbetween stations and the well head are measured and entered into thecomputer as a basis of computation. The transmitter is connected to thedrill collar dipole for continuous operation during the entire drillingoperation. The low-frequency electromagnetic signal from the drillcollar dipole passes relatively undistorted through the complexinhomogeneous media to each receiver antenna. A vertical magnetic dipolecomprising a small wire loop, buried or located at some depth beneaththe earths surface will produce an electromagnetic field on the earth ssurface if an alternating current is injected into the loop. Theconductivities of the overburden, which may be quite complex, willmodify the geometrical character of the vertical and horizontal magneticfield components observed at the surface. However, this effect is quitesmall provided the burial depths involved are small compared with thefree-space wavelength, or electrical skin depth.

The basic reference for the drill bit location system are:

l. The well head 2. The positions of the sensors with respect to thewell head 3. The local vertical passing through the positions of thesensors.

Sensors stations are initially set up at convenient locations on thecorners of a rough equilateral triangle, spaced approximately equallyfrom the well head at distances depending upon the intended maximumdepth of the bit.

The sensors are two-axis, mutually orthogonal receiving loops mounted inhighly accurate trunnions on a very stable base or platform. The maintrunnion provides means for rotation of the dual axis loop assemblyabout a vertical axis. The secondary trunnion provides means forrotation of the dual axis loop assembly about a horizontal axis.

The main trunnion is established in the local vertical by use of ahelium-neon gas laser interferometer/mercury pool optical level system,to within a few seconds of arc.

In operation, the main trunnion is rotated about the vertical axis toachieve a null in the horizontal sense loop. This establishes theazimuth angle in the horizontal plane between the well head referenceand the location of the buried dipole. The secondary trunnion is thenrotated about the horizontal axis normal to the bearing line to burieddipole until a null is achieved. This establishes a vertical angle ordip angle between the horizontal plane and a line passing through thelocation of the buried dipole.

The azimuth and dip angles are measured at all sensor sites, digitizedby shaft encoders attached to the trunnions and transmitted to thecomputer. The computer solves the multiple triangulation problem andestablishes position of the buried dipole in the coordinates desired.

It is an object of this invention to detect and plot the movement of atransmitter through an inhomogeneous solid media by transmitting anddetecting lowfrequency electromagnetic waves below 5,000 I-lz.

A further object of this invention is to provide a means to plot themovement of a drill bit as it moves into the ground without removing thedrill string.

Another object of this invention is to provide a transmitter powered bythe movement of the flow of fluids in the drill string.

An additional object of this invention is to provide two or threereceivers or transmitters just below ground level and the oppositecomponent at the head of the drill.

In accordance with these and other objects which will be apparenthereinafter, the instant invention will now be described with particularreference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1A is a plan view of a geometric illustration of a portion ofapplicants invention.

FIG. 1B is an illustration showing geometric arrangement of the threereceivers, the drill tower, drill string and drill collar dipole.

FIG. 2 is an elevation in partial cross section of the drill collarshowing the turbine driven alternator, transmitter compartment andantenna.

FIG. 3 is a block diagram of the receiver illustrating the receiverantenna, computer and display means.

FIG. 4 is a perspective view in partial cutaway of Applicants receiverantenna.

PREFERRED EMBODIMENT OF THE INVENTION FIGS. 1A and 1B show a cutawayportion of the earths surface, with the well head reference and sensorsA, B, and C embedded in the earths surface with associated equipmentresting on the earths surface and a drill string penetrating down intothe earth, terminating in the drill collar and drill bit. Attached tothe drill collar is an alternating dipole that radiates a SKHz or belowelectromagnetic wave which is detectable by sensors A, B and C. Acomputer (not shown) receives sensed information from which itdetermines the location of the drill bit relative to the well headreference. It has been determined that employment of a SKHZ or belowsignal allows for a very accurate triangulation of the received signalbecause minimum accurate triangulation of the received signal becauseminimum distortion of the directional propagation of the radiated waveis experienced as the wave proceeds from the dipole through variousstrata of the earths surface to the sensors.

The drill and transmitter assembly (FIG. 2) is comprised of a drillcollar removeably coupled at one end to the end of drill string 12 andat the other to a drill bit 13. The mud flow supply is provided throughinternal conduit 19 by struts 15. The alternator 14 is driven byrotating turbine blading 16 coupled to the alternator rotor (not shown).Fixed turbine blading 17 directs the flow of liquid in the internalconduit 19 onto the rotating turbine blading.

The hole cut out by drill bit 13 in the earth 24 provides for a mud flowreturn (indicated by arrows 23).

The dipole for radiating the 5 KI-Iz wave is provided by a pair ofelectrodes 21 circumferentially disposed about the drill collar llandelectrically coupled to the output of alternator 14 by electrical wires(not shown) in electrical conductor conduit 22.

FIG. 3 shows the sensing and computing systems comprising dual axis loopassembly 35 coupled to trunnions 36 moveably positionable by motors 34.The shaft encoders 33 send a signal back to computer interface 29disclosing the positon of the loop assembly.

Energy received in each loop from the dipole is sent to VLF amplifiers25 which are connected to null detectors 26, one output being to nullindicator 27 and the other to servo amplifiers 28 which drive motors 34.

Digital angular information is received from other sensors B and C (notshown) at the computer interface 29 from which the information is sentto computer 30, which solves the geometrical problem and displays theresults on display panel 32. Additional manual inputs 31 may be added tothe computer.

FIG. 4 shows a receiver antenna comprised of orthogonal loops 45 mountedon support bar 50 coupled to U-shaped moveable mount 44. A servo 46rotates the loops 45 through support 50. The entire antennae includingdome 41 is mounted on base 42. The dome 41 is filled with a liquid 43having the same conductivity as the surrounding earth, thus permittingmovement of the antenna with minimum wave distortion as it proceedsthrough the earths surface into the liquid 43. The antenna mount 44 isrotated by shaft 48 coupled through cover plate 47. The entire structureis anchored to base 42 by holding plate 49. In operation the antennaloops are rotated in three planes until a null signal is received. Theloop positions are received by the computer, and all antennae positionsare correlated to provide an accurate location position of the drillmounted transmitter.

In an alternate embodiment, the transmitter in the drill bit housing maybe replaced by a VLF receiver and the three surface receivers by threeVLF transmitters positioned in a triangular array. The transmitters areradiated individually during different time periods so that eachtransmitter antenna is moved until a signal null is indicated by thedetector in the drill bit housing. The received signals are transmittedup the drill pipe casing and sent to the computer along with signalsfrom shaftencoders on the antennae for position azimuth and depressionangles of the drill bit. The horizontal and vertical position of eachtransmitter antenna at signal maximum provides sufficient information todetermine drill bit location through triangulation. Again in thealternate embodiment the electromagnetic radiation is 5 K Hertz orbelow.

The antennae for transmitting as shown in the alternate embodiment areradio direction loops that are moveably mounted on a base and includeshaft encoders for vertical and horizontal position information andservo drive devices for positioning in different reference planes.

It is essential in either embodiment that both the transmitters or thereceivers are properly coupled to the ground surface in order to preventsignal path refraction distortion as would happen at the boundarybetween the earth and the atmosphere. In order to provide moveableantennae at the coupling point each antenna is submerged in a fluid, theconductivity of which is very close to that'of the earths surface atthat location.

With regard to system components, (FIG. 3) the computer interface 29 maybe a 3l6l model interface produced by Ocean Measurements, Inc. and madefor a Honeywell 316 computer. Position recorder 32 may be an XY recordermodel 7004B produced by l-lewlett-Packerd. Shaft encoders 33 that may beutilized are Series II, 2A s/11 from Computer Terminal Systems, Inc.while the amplifiers 25 are Khron-Hite tuneable amplifiers with VLFfilters.

In operation, the transmitter on the preferred embodiment may be analternator producing a power output in the range of five thousand wattsand having a frequency between to 5,000 Hz. The alternator is geared toa turbine blade that is placed in the mud supply conduit in the drillhead. The mud flowing downward through the conduit will turn the turbineblade to rotate the alternator to produce the output frequency. The headof the drill string will be the transmitting antenna. The receivingsystem will have three dual axis receivers, each optically surveyed inplace with respect to a horizontal azimuth reference. Each dual axisreceiver will also have its sensor oriented with respect to a verticalreference. The vertical reference will be established by laserinterferometer mercury level. The

antenna for each receiver will be properly coupled to the surface of theearth. Each receiver will determine the angle in the horizontal to thedrill bit and the angle in the vertical (dip or depression angle to thedrill bit). The intersection of the three lines determines theparticular location within the earth of the drill bit.

The computer is utilized to continuously compute and plot the locationof the transmitter and drill bit. The low-frequency electromagnetic waveis relatively unaffected as it travels through the various layers ofmaterial between the transmitter and the receiver because smallvariations in media densities are negligible at these electromagneticfrequencies.

The instant invention has been shown and described herein in what isconsidered to be the most practical and preferred embodiment. It isrecognized, however, that departures may be made therefrom within thescope of the invention and that obvious modifications will occur to aperson skilled in the art.

What I claim is:

1. An apparatus for locating a drill bit within the earths crustrelative to a predetermined reference position comprising:

a low frequency electro-magnetic wave transmitter within the earth fortransmitting an output signal below 10,000 Hertz;

a power supply connected to said transmitter;

at least two directional indicating low frequency receivers inconductive communication with the earth for detecting the transmittedlow frequency signals; and

analyzing means coupled to said receivers for analyzing the lowfrequency received signals providing information giving the referencelocation of said transmitter relative to said predetermined referenceposition; and

a drill rig including a drive means, a drill string connected to saiddrive means, and a drill bit connected at the free end of said drillstring, said low frequency electro-magnetic transmitter coupled to saiddrill string, adjacent said drill bit.

2. A drill location apparatus, as set forth in claim 1, wherein saidtransmitter includes:

an alternator;

a turbine driveably connected to said alternator;

a mud supply conduit coupled within said drill string,

said turbine disposed within said mud supply conduit.

3. A drill location apparatus as set forth in claim 2 including:

indicating means coupled to said analyzing means for providing a visualdisplay of said drill bit location.

4. A drill bit location apparatus as set forth in claim 3, wherein:

said receivers include a housing in contact with said earth surface,

. a fluid medium within said housing having a conductivity similar tothat of the surrounding earth, said receiver antennas immersed in saidmedium.

5. A drill location apparatus as set forth in claim 4, wherein:

the lower end of said drill string is connected to the transmitteroutput to cause the lower end of the drill string to act as anelectrical dipole antenna. 6. A method for detecting the location of adrill bit within the surface of the earth by transmitting low frequencyelectro-magnetic wave energy with reference to a known predeterminedreference location comprising the steps of:

transmitting a low frequency electro-magnetic wave below 5,000 Hertzwithin the earths surface from a drill bit located within the earthssurface while simultaneously moving the drill bit within the earthssurface to perform drilling; receiving the transmitted low frequencyelectromagnetic energy within the earths surface; and comparing thereceived signals from the receivers with a known reference pointlocation signal thereby determining the location of the transmittingsource relative to the known reference point.

7. An apparatus for locating a drill bit within the earths crustrelative to a predetermined reference position comprising:

a low frequency electro-magnetic receiver within the earth for receivingan electro-magnetic signal below 10,000 Hertz;

at least two low frequency electro-magnetic transmitters in conductivecommunication with the earths crust for transmitting low frequencysignals;

a power supply connected to said transmitters;

an analyzing means coupled to said receiver for analyzing the lowfrequency received signals for providing information giving thereference location of said transmitters relative to said predeterminedref erence location; and

a drill rig including a drive means, a drill string connected to saiddrive means, and a drill bit connected at the end of said drill string,said low frequency electro-magnetic receiver coupled to said drillstring.

1. An apparatus for locating a drill bit within the earth''s crustrelative to a predetermined reference position comprising: a lowfrequency electro-magnetic wave transmitter within the earth fortransmitting an output signal below 10,000 Hertz; a power supplyconnecTed to said transmitter; at least two directional indicating lowfrequency receivers in conductive communication with the earth fordetecting the transmitted low frequency signals; and analyzing meanscoupled to said receivers for analyzing the low frequency receivedsignals providing information giving the reference location of saidtransmitter relative to said predetermined reference position; and adrill rig including a drive means, a drill string connected to saiddrive means, and a drill bit connected at the free end of said drillstring, said low frequency electro-magnetic transmitter coupled to saiddrill string, adjacent said drill bit.
 2. A drill location apparatus, asset forth in claim 1, wherein said transmitter includes: an alternator;a turbine driveably connected to said alternator; a mud supply conduitcoupled within said drill string, said turbine disposed within said mudsupply conduit.
 3. A drill location apparatus as set forth in claim 2including: indicating means coupled to said analyzing means forproviding a visual display of said drill bit location.
 4. A drill bitlocation apparatus as set forth in claim 3, wherein: said receiversinclude a housing in contact with said earth surface, a fluid mediumwithin said housing having a conductivity similar to that of thesurrounding earth, said receiver antennas immersed in said medium.
 5. Adrill location apparatus as set forth in claim 4, wherein: the lower endof said drill string is connected to the transmitter output to cause thelower end of the drill string to act as an electrical dipole antenna. 6.A method for detecting the location of a drill bit within the surface ofthe earth by transmitting low frequency electro-magnetic wave energywith reference to a known predetermined reference location comprisingthe steps of: transmitting a low frequency electro-magnetic wave below5,000 Hertz within the earth''s surface from a drill bit located withinthe earth''s surface while simultaneously moving the drill bit withinthe earth''s surface to perform drilling; receiving the transmitted lowfrequency electro-magnetic energy within the earth''s surface; andcomparing the received signals from the receivers with a known referencepoint location signal thereby determining the location of thetransmitting source relative to the known reference point.
 7. Anapparatus for locating a drill bit within the earth''s crust relative toa predetermined reference position comprising: a low frequencyelectro-magnetic receiver within the earth for receiving anelectro-magnetic signal below 10,000 Hertz; at least two low frequencyelectro-magnetic transmitters in conductive communication with theearth''s crust for transmitting low frequency signals; a power supplyconnected to said transmitters; an analyzing means coupled to saidreceiver for analyzing the low frequency received signals for providinginformation giving the reference location of said transmitters relativeto said predetermined reference location; and a drill rig including adrive means, a drill string connected to said drive means, and a drillbit connected at the end of said drill string, said low frequencyelectro-magnetic receiver coupled to said drill string.